JPH03120920A - Optical reception circuit - Google Patents

Abstract

PURPOSE:To prevent the band deterioration in an avalanche photodiode with simple constitution by providing a voltage holding circuit holding an output voltage of a voltage control circuit to be a prescribed value or over. CONSTITUTION:When an input level of an optical signal is increasing, a bias voltage gets lower, band deterioration takes place in a reception signal of an avalanche photodiode 1 but the reduction of a bias voltage to be a prescribed level or below is blocked by a voltage holding circuit 8. That is, a prescribed voltage signal resulting from dividing an output voltage of a high voltage generating circuit 7 with resistors 8b, 8c is obtained at a connection midpoint of the resistors 8b, 8c and even when a collector level of a transistor(TR) 6a in a voltage control circuit 6 is decreased, a level at a cathode side point (b) of diodes 8a, 8d (that is, a bias voltage) is not lowered than the divided voltage signal. Thus, a bias voltage of the avalanche photodiode 1 is not lowered than the voltage division signal resulting from dividing an output voltage of the high voltage generating circuit 7 with the resistors 8b, 8c and the band deterioration in the reception signal is blocked.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical signal receiving circuit using an avalanche 2-odd diode. As a signal receiving circuit, JP-A-63-2
As described in Japanese Patent No. 15126, a circuit as shown in FIG. 2 has been known in the past. In this figure 2,
1 indicates an avalanche photodiode, and the output signal of this avalanche photodiode 1 is sent to a preamplifier circuit 2.
and is supplied to the peak value detection circuit 4 via the variable gain amplifier circuit 5, and the detection signal of this peak value detection circuit 4 is supplied to one input terminal of the error amplifier circuit 5. In this case, the variable gain amplifier circuit 3 , No. 2 from the preamplifier circuit 2 is equalized and amplified, and the gain is changed so that the output voltage is constant.Then, the reference voltage signal obtained at the reference voltage signal input terminal 5a is The voltage control circuit 6 is supplied with the high voltage from the high voltage generation circuit 7 to supply the error signal output from the error amplification circuit 5 to the other input terminal of the error amplification circuit 5 and to the voltage control circuit 6. A signal is supplied, the voltage value of this high voltage signal is controlled by a voltage control circuit 6 based on an error signal, and the controlled high voltage signal is supplied to the avalanche photodiode 1 as a bias voltage.

[vjA problem that the invention attempts to solve]

In the circuit configuration shown in FIG. 2, when the input level of the optical signal to the avalanche photodiode 1 is high, the voltage control circuit 6 works to lower the bias voltage of the avalanche photodiode 1.

When the bias voltage decreases in this way, there is a problem in that the output signal of the avalanche photodiode 1 suffers from band deterioration. In order to prevent this band deterioration, it has been proposed that K be provided with a comparison/judgment circuit that, for example, compares the output signal of the error amplifier circuit with a reference voltage signal and controls the high voltage generation circuit according to the comparison result. When a comparison/determination circuit is provided in this way, there is a problem in that the circuit configuration becomes complicated.

An object of the present invention is to prevent band deterioration of an avalanche photodiode with a simple configuration.

[Means for Solving the Problems] In order to achieve the above object, the optical receiving circuit of the present invention is provided with a voltage holding circuit that holds the output voltage of the voltage control circuit that controls the bias voltage above a certain level. be.

[Effect]

According to this configuration, even if the voltage control circuit lowers the output voltage when the input level of the optical signal to the avalanche photodiode is high, the voltage holding circuit maintains the bias voltage above a certain value, and the avalanche photodiode Bandwidth degradation is prevented.

〔Example〕

An embodiment of the optical receiving circuit of the present invention will be described below with reference to FIG. In FIG. 1, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In this example, the output signal of the avalanche photodiode 1 via the preamplifier circuit 2 and variable gain circuit 3 is
A peak value detection circuit 4 detects the peak value. Then, the error amplifier circuit 5 detects an error between the reference voltage obtained from the reference voltage signal input terminal 5aK and the peak value detection output, and supplies the error signal to the voltage control circuit 6. In this case, the error signal is supplied to the P-X IIC of the NPN transistor 6a constituting the voltage control circuit 6. And this transistor 6
The emitter of a is grounded via the resistor 6b. Also,
The output voltage of the high voltage generation circuit 7 is supplied to the collector of the transistor 6sL via the resistor 6c.

In this example, the voltage holding circuit 8 is provided.
In other words, the transistor 6a O2 collector is connected to the anode of the diode 8a that constitutes the voltage holding circuit 8, and the cathode of this diode 8a is connected to the avalanche photodiode 1.In addition, the output side of the high voltage generation circuit 7 is , resistors 8b and 8c forming the voltage holding circuit 8
grounded through a series circuit of 8b and 8b.
Connect the middle point of connection c to the anode of diode 8d.

The cathode of this diode 8d is connected to the avalanche photodiode 1.

The operation of the receiving circuit with this configuration will be explained below. For example, if a high-level optical signal is input to the Alapan shear odd diode 1 (at this time, the output voltage of the peak value detection circuit 4 increases), the error amplifier circuit The error output voltage of No. 5 also increases. Due to this increase in the error output voltage, a pace current flows through the transistor 6a in the voltage control circuit 6, and the collector potential of the transistor 6a, which is the bias voltage of the avalanche photodiode 1, decreases. Due to this decrease in the collector potential (ie, bias voltage), the multiplication factor of the avalanche photodiode 1 decreases, and the output of the variable gain amplifier circuit 5 is kept constant.

In this way, as the input level of the optical signal increases, the bias voltage decreases, causing band deterioration of the avalanche photodiode 1. In this example, the voltage holding circuit 8 prevents the bias voltage from dropping below a certain value, i.e. resistor 8'b
A constant voltage signal obtained by dividing the output voltage of the high voltage generation circuit 7 by the resistors 8b and 8a is obtained at the connection midpoint a of the high voltage generating circuit 7 and 8c. The potential (that is, the bias voltage) at the point on the cathode side of 8d (that is, the bias voltage) also does not drop due to this divided voltage signal. Therefore, the bias voltage of the avalanche photodiode 1 is equal to the divided voltage signal divided by the resistors 8b and 8C. The band quality of the received signal is not degraded, and the band deterioration of the received signal is prevented.
In the table, when the optical input level is high, the diode 8a
, is provided to prevent the divided voltage signal from flowing to the collector side of the transistor 6a, and the diode 8d prevents the collector current of the transistor 6a from flowing to the resistor 8c@ when the optical input level is low. It was established for the purpose of

〔Effect of the invention〕

According to the optical receiving circuit of the present invention, with a simple circuit configuration that only includes a voltage holding circuit that outputs a constant voltage signal, it is possible to prevent band deterioration of the received signal due to a drop in the bias voltage of the avalanche photodiode. The dynamic range of the receiving circuit can be expanded.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the optical receiving circuit of the present invention;
Figure 2 is a configuration diagram showing an example of a conventional optical receiver circuit◎

Claims (1)

[Claims] 1. An avalanche photodiode that converts an optical input signal into an electrical signal, an equalization amplifier circuit that converts a current signal from the avalanche photodiode into a voltage signal, and a detection circuit that detects the output level of the equalization amplifier circuit. and a high voltage generation circuit that supplies a bias voltage to the avalanche photodiode, and a voltage control circuit that controls the bias voltage generated by the high voltage generation circuit based on a detection signal of the detection circuit, wherein the voltage control circuit includes: An optical receiving circuit characterized by being provided with a voltage holding circuit that holds the output voltage of the circuit above a certain level.